Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance. Such changes in capacitance can indicate a touch event or the presence of ridges and valleys of a fingerprint. Touch sensing may be used for applications on a variety of user interface devices, such as mobile handsets, personal computers, and tablets. The use of capacitance sensing for touch detection may allow for a touch sensor (also referred to herein as an electrode, a sensor, etc.) to be placed in or under the surface of a user interface device with a great degree of configurability. In one embodiment, a touch sensor may not be specific to a single location for all devices. Rather, touch sensors may be disposed where convenient to the industrial design of the device.
Capacitance-based touch sensors work by measuring the capacitance of a capacitive sense element and sensing a change in capacitance indicating a presence or absence of an object (e.g., a finger or a ridge or valley of a fingerprint). When an object comes into contact with, or is in close proximity to a touch sensor, the capacitance change caused by the object is detected. The capacitance change of the touch sensor can be measured by an electrical circuit and converted into a digital capacitance value.